Fix mSubtractDisplacement when recatching

Previously we correctly set mSubtractDisplacement when re-catching
during the SETTLING state, but then immediately overrode it to be
+/-mTouchSlop.

Test: Swipe up to all apps, catch it by touching down during the
transition, ensure there's no jump when starting to move again.

Change-Id: I5d543e8a8b027b68bafb26b752e70862f6ae0777